The present invention generally relates to the chemical treatment of casting slurries and cores, and more particularly to the recovery of Y.sub.2 O.sub.3, from investment casting slurries and investment casting cores.
Yttrium oxide (Y.sub.2 O.sub.3) is an important and useful metal casting refractory. It is thermodynamically stable in the presence of most reactive engineering metals including titanium, titanium alloys, and columbium (niobium). General information regarding Y.sub.2 O.sub.3 metal casting processes is presented in Feagin, R. C., "Casting of Reactive Metals into Ceramic Molds", Report of Sixth World Conference on Investment Casting, pp. 4:01-4:13, 1984; and Calvert, E. D., "An Investment Mold For Titanium Casting", United States Department of the Interior (Bureau of Mines), Report of Investigations No. 8541, 1981.
The use of Y.sub.2 O.sub.3 as a refractory material in both investment and core casting processes normally involves the production of a slurry containing both Y.sub.2 O.sub.3 and a hydrolyzed binder. An example of such a slurry is described in U.S. Pat. No. 4,703,806, of Lassow, et al. Most often, silica binders are used, such as tetraethyl ortho silicate. Once the casting process is completed, the slurry is usually discarded. However, this is undesirable for both financial and environmental reasons. Recycling of the slurry to reclaim Y.sub.2 O.sub.3 would offer a significant cost savings, and eliminate disposal problems.
The present invention involves a method whereby Y.sub.2 O.sub.3 can be reclaimed from used casting slurries and cores which contain Y.sub.2 O.sub.3 in combination with a binder. The method is highly efficient, and results in the recovery of up to 90% or more of the Y.sub.2 O.sub.3 originally contained in the slurry. Also, the recovered Y.sub.2 O.sub.3 has a purity level of nearly 100%. This is accomplished using a minimal number of process steps, as described in detail below.